DESCRIPTION (Applicant's Description) Breast and ovarian cancer rank second and fourth respectively in mortality in the United States with greater than 200,000 new cases reported each year. Approximately 5 percent to 10 percent of these cases result from a hereditary predisposition with germline mutations conferring autosomal dominant susceptibility. The alteration and subsequent inactivation of one gene, BRCA1, is believed to be present in 50 percent and 90 percent of cancer families with increased incidence of early-onset breast and ovarian cancer respectively. Female carriers in these families have an estimated 85 percent life long risk of contracting cancers associated with the BRCA1 gene. Over 100 mutations have been identified including missense, frameshifts and splice-site alterations, 85 percent of which result in premature termination of protein formation resulting in truncation. Presently, much time and expense is incurred to identify gene mutations through DNA sequencing methods. More cost-effective methods are required to screen female and male members of these families for heritable BRCA1 alterations. We used antibodies specific for both amino acid terminals of the BRCA1 protein, to demonstrate BRCA1 protein truncations by immunohistochemical analysis of matched ovarian tumor and normal tissue. In normal tissue, BRCA1 truncation is indicative of the presence of a germline mutation. We also present data demonstrating expression of BRCA1 protein in human buccal cells using the same antibodies and presence of BRCA1 mRNA by RT-PCR. The proposed study will determine whether heritable BRCA1 gene alterations may be detected in buccal cells by using quantitative immunohistochemical analysis, and will evaluate the sensitivity of this assay among individuals in this study. Mutations will be confirmed by gene sequencing of matched blood cell DNA. A sensitivity of greater than 75 percent would establish a basis for further development of this assay as a noninvasive, cost effective screening test for male and female carriers of BRCA1 mutations.